Hmm known combinations that have worked for me:

+ old machines - DEL key
+ newer and average machines - F2
+ laptops - F1 [if they have a BIOS]
+ dual-cpu I have running a pair of Katmai procs [P3s @ 450 MHz each]: well, one is F2 for regular BIOS but it has another utility that gets called through Ctrl + C

I'm thinking it should be DEL if it isn't F2 though, if you have a 'boot logo' press TAB and maybe it'll go away... or yank the F2/DEL keys and maybe you get lucky